The present invention relates to a security device for preventing unauthorized use of a trailer or other vehicle having a coupling pin used to couple the trailer to a tractor or another vehicle, and to a locking device for the security device.
Coupling devices for coupling a trailer to a tractor typically include a coupling pin attached to the front of the trailer and a complementary receptacle attached to the rear of the tractor which releasably engages the trailer coupling pin while allowing relative pivoting of the trailer and tractor. A coupling device in wide use today comprises a pin referred to as a king pin depending from the front of trailers and a complementary skid plate receptacle or fifth wheel mounted to the rear of tractors. The king pin and skid plate are standardized so that any trailer having a king pin may be coupled to any tractor having a complementary skid plate. Frequently, trailers are uncoupled from tractors, for example, during loading and unloading, for storing trailers when they are not in use, or for using tractors independently of trailers, and left unattended. In such instances, an unauthorized person with a tractor having a complementary skid plate for the trailer king pin may simply couple to the trailer, connect the air hoses to release the trailer brakes and haul the trailer away.
To prevent unauthorized use of trailers having a coupling pin, security devices are known which are secured to the trailer coupling pin so as to prevent coupling of the trailer coupling pin to a complementary receptacle on a tractor. Such security devices include a locking device by means of which the security device is locked to the trailer coupling pin. Security devices of that type are described in U.S. Pat. Nos. 2,554,306 (Mack) issued May 22, 1951; 2,641,124 (Gallagher et al.) issued June 9, 1953; 2,755,655 (Maffey, the applicant herein) issued July 24, 1956; 3,415,085 (Eble, Jr.) issued Dec. 10, 1968; 3,798,938 (McCullum) issued Mar. 26, 1974, and 4,031,727 (DeGroat et al.) issued June 28, 1977; and Canadian Patent No. 689,737 (Dalton) issued June 30, 1964.
Prior security devices of the type described in the aforementioned patents were not entirely satisfactory for a number of reasons. In many prior security devices of that type, the lock cylinder, i.e., that part of the locking device which receives a key and is actuable between locked and unlocked conditions thereof, is exposed so that it could be easily tampered with. Thus, the lock cylinder could be engaged, for example, by drilling into it and connecting a pulling device to it, and forcibly retracted from the security device. U.S. Pat. No. 3,798,938 (McCullum) discloses a security device including a guard plate inserted across an opening for inserting the lock cylinder into the security device. The guard plate carrys a rotatable key-slotted disk in an opening coaxial with the key plug of the lock cylinder, which protects the key plug from drilling.
Some prior security devices of the general type described above include a locking device having a spring loaded bolt mechanism. See, for example, U.S. Pat. Nos. 3,415,085, 3,798,938 and Canadian Patent No. 689,737. It was thus possible to lock such a security device to a trailer coupling pin without the use of a key, which may have or may become lost or misplaced.
It is also possible for security devices of the general type described above to be attached to the trailer coupling pin but not positively locked thereto, while the security device externally appears to be locked to the trailer couping pin. Thus, it was possible for a trailer to be left unattended with a security device held by, but not locked to, the trailer coupling pin.
Applicant's prior U.S. Pat. No. 2,755,655 discloses a security device having a locking device slidably held in an aperature in the security device, the locking device being slidably movable into engagement with the trailer coupling pin for locking the security device to the coupling pin, and slidably movable out of engagement with the coupling for enabling removal of the security device from the coupling pin. That locking device included a lock cylinder which was almost fully exposed, and which was therefore accessible for tampering.
There is thus a need for a security device for vehicles such as trailers having a coupling pin which avoids the drawbacks described above, provides improved security and is of simple construction.